After single point re-cutting the action threads, the barrel tenon threads will be a larger diameter. Meaning the I.D. hole in the lug will have to be opened up to give appropriate clearance. In the past smiths set the lug up on a mill, dialed it in and machined for clearance. Accurate but very time consuming for an operation that makes you no money. Just part of the job.
This jig works in a 3 jaw chuck. It takes about 5 minutes to clamp the jig in a 3 jaw, clamp and center lug with the tailstock, dial in with a dial test indicator and then bore diameter.